1. Field of the Invention
The present invention generally relates to photothermal inspection of surface welds and more particularly to remote phtothermal inspection of welds in reactor elements such as control rod nozzles.
2. Description of the Prior Art
Nuclear reactors have a reactor cover or closure head through which a series of openings having tubes extending into the inside surface of the reactor are welded to the closure head by J-groove welds. These tubes have control rod drives (CRD) and instrumentation packages sealably extending into the reactor internals. These J-groove welds must be inspected during reactor shut down for any cracks that may have developed in the welds. Such inspections must be made from beneath the reactor head with the head on a supporting head-stand during normal refueling periods. Standard nondestructive examination techniques such as eddy current and die-penetrant examinations are currently the normal inspection approach. Since the high radiation in the reactor prevents personnel from entering the reactor to perform such testing, various robotic elements are used to remotely access these welds with the mentioned nondestructive testing machinery. The known testing equipment require a close proximity or actual contact to the tested weld surface which is difficult to achieve with the robotic delivery devices and the remotely controlled tools used to access the welds.
Thus some form of nondestructive remote testing of these welds was needed which did not require close proximity or contact with the welded surface and the exact robotic manipulation associated therewith which is difficult to implement.
Generally photothermal weld testing is known and is described in various patents. As an example, U.S. Pat. No. 4,854,724 teaches the use of a non destructive examination (NDE) technique using IR thermography to determine weld integrity by detecting infrared radiation emitted from the weld 1T surface which has be en preheated by a heat source. The application is to determine weld integrity in aircraft and does not recognize the problems associated with checking nuclear reactor welds with internally located robotics.
U.S. Pat. No. 6,000,844 teaches a remote portable NDE technique for determining the integrity of a material surface using a moving heat source and an I-R camera to produce a thermal image of the surface that shows defects as surface temperature deviations but again fails to recognize checking nuclear reactor internal welds using robotics.
U.S. Pat. No. 6,329,635 teaches a laser welding monitoring technique using IR emission. The patent shows that it is known to use laser heat sources in combination with IR thermographic imaging techniques but fails to teach any nuclear reactor weld checking techniques inside the reactor.